Development of Versatile Area Gamma Monitor for Radiation Industries

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 09 Issue: 06 | June 2022 www.irjet.net p-ISSN: 2395-0072
© 2022, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page 160
Development of Versatile Area Gamma Monitor for Radiation Industries
Ronie Adhiraaj Ghosh1
1Board of Radiation and Isotope Technology, Sector-20, Vashi, Navi Mumbai-400703, Maharashtra, India
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Abstract - Radiation Safety is prime importance of any radiationrelated industryfor protectionoftheworkersand public. Itcan
be achieved by Radiation Monitoring instruments that always stand guard measuring radiation in ambience and by alerting
people and enabling preventive measures in timely fashion to mitigate the causes and prevent any harmful effect on public,
workers or property due to radiation. This article highlights the development of Industrial Area Gamma Monitors that are
specifically tailor made for Radiation Industries that not only checksforambientradiation andalertsus, alsothesehaveprovisions
for Industrial standard of communication protocols to interface with Industrial automation devices.
1. INTRODUCTION
Use of Area Radiation Monitor is to detect gamma radiation dose rate above a certain threshold values to facilitate the experts
in mitigating the source causes and protecting personnel from over exposure. For general public the exposurelimitis1mSv (1
milli Sievert) and for occupational radiation worker is 30mSv (30 milliSievert)annually[5].TheconceptofALARA[5] (AsLowAs
Reasonable Achievable) shall be followed. For this Radiation monitoringinstrumentsarerequiredandonesuchinstrumenti.e.
Area Radiation Monitor that has been developed to alert and avert the unnecessary exposure to people. A radiation monitoris
first line of defense against unnecessary radiation exposure. Safety and precaution shall be prime concern of any Radiation
industry. To make sure we must use instruments in the field and ensure safety of workers as well as general population. Area
Radiation Monitors are based on GM Tube or Geiger Muller Tubes. [2]
1.1 Concept
GM tube is gaseous ionization detector used to detect nuclear radiationbyusing TownsendAvalancheeffect. Thetubecontains
a gas mixture at low pressure of about 0.1 atm. The chamber contains two electrodes as shown in Figure 1.
Fig.1 A GM tube construction
The wall construction of the tube is metal or glass with inside surface coated with a metal to form the cathode, while
the anode is a concentrically placed Tungsten wire separated by cathode by an insulator in the centre of the tube.
Fig. 2 A small sized GM Tube LND7121 with energy compensation shield [4]

Fig. 3 A Longer GM Tube with higher sensitivity LND7807 with energy compensation shield [4]
When ionizing radiation strikes the tube, some molecules of the gas are ionized, either directly by the incident radiation or
indirectly by means of secondary electrons produced in the metal walls of the tube due to photoelectric effect. Either ways
positive charged ions and negative charged electrons are produced, or what we commonly knowas ionpairsinthe fill gas.Due
to high electric field created by high voltage DC application across the GM tube terminals, an avalanche region exists close to
the anode where the electrons gain sufficient energy and accelerateathighspeedtohit andionizeadditional gasmoleculesand
create a large number of electron avalanches which multiply along the anode and effectively throughout the entire GM tube
region. This is the Townsend Avalanche or Gas multiplication effect which gives the tube its key characteristic to produce a
significant output current pulse from a single ionizing event. This short and spiked pulse of current can be counted as an
event in the form of a voltage pulse developed across an external electrical load resistor as in Fig. 4. This can be in the
magnitude of few volts. The voltage pulse is signal processed to give it a proper logic signal shape that makes electronic
processing simple by the digital counters implemented in the system. The pulsetrainis countedfora specifictime windowand
is translated in CPS/CPM or Counts per Second/Counts per Minute and is calibrated in terms of mR/hr (milliRoentgen per
hour) or µSv/hr (microSievert per hour) which denote the radiation dose rate.Thesensitivityofa GMtubeisspecifiedinterms
of mainly CPS/mR/hr. e.g in Fig. 2 LND7121 has sensitivity of 18cps/mR/hr and in Fig. 3 LND7807 has sensitivity of
150cps/mR/hr.
2. Methodology
The Area Radiation Monitor, which is an instrument for measuring dose rate in the vicinity. It denotes Radiation dose rate in
terms of either mR/hr or µSv/hr. The instrument usesa veryruggedandwell knownGeiger-Mullertube(GMTube).Apartfrom
that High Voltage DC source for biasing the GM tube. Pulse shaper and counter circuit has been implemented.
Fig. 4a

Fig. 4b Pulse Output of GM Tube and logic level translation of signal shaper unit.
In one model of GM Tube based Area Gamma Monitor, Microcontroller based LCD and optional Seven Segment readout and
alarm generation is incorporated. Industrial communication modulessuchasRS-485basedMODBUSserial communication,4-
20mA industrial current loop, TCP/IP Ethernet and TCP MODBUS are implemented. Apartfromthatpotential freerelayoutput
and Audio Visual alarm setup is also implemented in the instrument.
The GM Tube used is LND7121 that works from a range of 450V to 600V high voltage DC(HVDC). The HVDC circuit has been
constructed using a boost converter that converts 9V DC to 500V DC and is a low ripple DC Voltage [1]. When radiation is
incident on GM tube and inside the pulse output can be seen in Fig. 4. The pulses are processed and converted into Logic level
compatible pulses using pulse shaper circuit as in Fig. 4, so that it can be read by Microcontroller based Counter assembly as
CPM or CPS, as well as dead time compensation for GM tube is done [3]. The dead time is the time during which, after the
detection of an event, the GM counter cannot detect a subsequent event. The Microcontroller contains calibration data that
converts the respective counts in terms of mR/hr or µSv/hr. There is user set Alarm radiation threshold in the system, and if
the incident radiation crosses this limit the Logic relay is activated for safety interlocking as well as the Alarm LED starts to
blink and Alarm buzzer starts to sound. The entire data can be seen on Instrument local display that consists of a very high
contrast OLED display screen as seen in Figure 7. A very reliable 4-20mA current loop module has been implemented for the
instrument which is very useful for gathering instrument parametervaluetoa centralizedPLCbasedsystemwithAnalogInput
modules which would help to gather all the Plant Radiation data on to a single system and display on SCADA. The instrument
also includes RS-485 based serial communication module that isessential forIndustrial digital serial communication.However
these modules are optional and maybe implemented as per user's choice. Operations flowchart has been depicted in Fig. 5.
Further there was development of Area Gamma Monitor with Ethernet communication interface to implementMODBUSTCP
and TCP/IP which give this instrument a versatility of mounting the same in industry as well as in Civilian area. It denotes
Radiation dose rate in terms of either mR/hr or µSv/hr and generates local soundandlightbasedalarmifradiation doserateis
high beyond permissible limits for various zones set as threshold. It also communicates the Radiationdoseratedata andother
instrument parameters through TCP/IP Ethernet. This particular communication protocol was chosen as there is Ethernet
connectivity almost anywhere now a days, namely, offices, ports,labsetc. Propersignal isolationhasbeenimplementedinboth
the instruments models for reliable operation in industrial environment.

Fig. 5 Operations Flow Chart for the working of the Area Gamma Monitor models.
or Ethernet Module

3. Implementation
A complete Instrument Block diagram for model with RS-485 MODBUS and 4-20mA communication has been showninFig.6.
Fig.6 Block diagram of model with RS-485 MODBUS and 4-20mA current loop outputs

The printed circuit board for the same model as in block diagram of Fig. 6 is shown in Fig. 7.
Fig.7 Assembled printed circuit board for one model with RS-485 MODBUS and 4-20mA current loop outputs.
Many iterations in design has been done to make HVDC power supply efficient for very high dose rate, proper component
placement modifications has been done in order to reduce interference noise of DC to DC boost module, proper component
selection for reliable data communication and alarm.
Use of OLED display in place LCD display has been done in order to provide very highcontrastdisplayfor easyreadabilityfrom
all angles and at a given minimum distance as in Fig. 8
The Calibration graph has been plotted between CPS and Dose rate as per Figure 8 is found to be almost linear for a rangeof0-
100mR/hr.
Fig. 8 Instrument readout screen with OLED display for high contrast.

Fig 9. Plot of CPS vs Dose Rate in mR/hr during calibration of model with RS-485 MODBUS and 4-20mA current loop
outputs
The Calibration was done for a range of 0mR/hr to 100mR/hr Fig. 9 and after that instrument prototype was found to be
accurate within 10% of Actual reading which is acceptable.
The Microcontroller contains calibration data that converts the respective counts intermsofmR/hror µSv/hr.The calibration
has been done at Calibration lab with Cesium source. There is preset Alarm radiation threshold in the system, and if the
incident radiation crosses this limit the Logic relay is activated for safety interlocking as well as the Alarm LED starts to blink
and Alarm buzzer starts to sound. The entire data can be seen on Instrument local display that consists of a very high contrast
OLED display screen as seen in Fig. 8 Further Ethernet communication capability over TCP/IPcommunicatessystemdata and
parameters to a central logging server running MySQL database where all the data is logged after sampled periodically, say
after 15 seconds time gap. User can access the data and may visualize the same in graphs that are updated continuously.
Fig. 10 Mounting scheme of Ethernet based Area Gamma Monitor
Instrument
Ethernet N/W
Webserver with
Database/Industrial
Server for MODBUS
User Portal

Fig. 11 Assembled Printed Circuit Board for the TCP/IP Ethernet and MODBUS Ethernet based model of Area Gamma
Monitor
Fig. 12 Block diagram of model with TCP MODBUS or TCP/IP Ethernet interfacing

In Fig. 10 we can see the scheme of mounting the instrument in the field. As this instrument is Civilian in nature the mounting
and interfacing shall be compatible with Ethernet Network. The Instrument has local display/alarmbuzzerandlightaswell as
TCP/IP Ethernet communication. The is provision for a Central data logging server runningMySQLdatabaseandData Logging
application in PHP that pulls the data from the instrument automatically after giventimedelay.Thetimedelaycanbevariedas
per user requirement. The network parameters and instrument parameters can be modified using web browser. The
instrument has capability of pushing the data over database irrespective of sampling time in case when radiation dose rate is
higher than threshold. The central server may also have graph plotting application and report generation of any particular
instrument. The entire unit was fabricated by soldering components on printed circuit board and enclosing the same in a
general purpose polymer box. The control button panel and display was fixed on the top cover.
Fig. 13 Plot of CPS vs Dose Rate in mR/hr during calibration of model with Ethernet interface
The Calibration was done for a range of 0 to 10mR/hr and residual errors were adjusted within the software asinFig.13,after
that instrument prototype was found to be accurate within 5% of Actual reading which is acceptable.
4. Conclusion
The accuracy of the instruments were initially ±10% , which is expected to degrade once the instrument ages. To mitigate this
the instruments have to be recalibrated over a period of 6 months to 1 year subject to the accuracy if it is better than
acceptable limit. Higher sensitivity GM tube may be used in case of areas where high resolution of Radiation detection is
required. Since the instrument fabrication is modular over the printed circuitboards,thefeaturesimplementedlikeRS-485,4-
20mA loop, Ethernet, Audio Visual alarm, potential free Relay output etc. maybe kept optional. This implementation adds
versatility to further research, fabrication, production and deployment of Geiger Muller tube based radiation detectors in
Radiation industries.
ACKNOWLEDGEMENT
Calibration Services
Board of Radiation & Isotope Technology, BRIT/BARC Vashi Complex, Sector 20 Vashi, Navi Mumbai-400703
REFERENCES
[1] Gandhiraj, Prasanna & Jayapandian, J. (2014). An embedded read-out for GM counter. international journal of
instrumentation technology. 1. 228-240. 10.1504/IJIT.2014.065180.

[2] Remon, Newaz & Zakir, M. (2018). Build very simple design and cost effective geiger-muller counter. Research Journal of
Applied Sciences. 31. 1-10.
[3] Geiger Muller Tube Theory
(https://qa.ff.up.pt/radioquimica/Bibliografia/Diversos/geiger_tube_theory.pdf, www.centronic.co.uk)
[4] Mohamed Noor, O., “Development of energy compensated Geiger Muller detector based on the T2416A Canberra Co. GM
detector”, MsT, 2013.
[5] Radiological Protection Principles, AERB https://www.aerb.gov.in/english/radiation-protection-principle

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